In the semiconductor industry, epitaxy is the growth of a crystalline layer, typically from a seed layer in a seed window area. A seed window area refers to the two-dimensional size of an exposed surface where an epitaxial layer is to be grown. With the scaling down of device dimensions, such as for three-dimensional (3D) NAND flash memory devices, the seed window area is also reduced. Seed window area dimensions and surface deformations can greatly affect the epitaxial growth rate of an epitaxial layer in the seed window area, which has been described as a loading effect.
The loading effect, which is also referred to as a local loading effect or a pattern loading effect, occurs due to a difference in pattern density. The phenomenon occurs upon simultaneous epitaxial growth in a low pattern density region (i.e., larger seed window area) and in a high pattern density region (i.e., smaller seed window area). Depending on the local pattern density, the epitaxial growth rate is different and causes a non-uniformity in the thickness of the grown epitaxial layer. The non-uniformity in epitaxial layer thickness between low and high pattern density regions makes device processing difficult to control and may adversely affect device performance.